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Why is a stable frequency important for the power system?

The frequency is an indicator of the balance between electricity consumption and production.

The frequency is kept stable using reserves such as power plants, demand facilities and energy storages
that can adjust their power exchange with the grid. However, the reserve units we currently have
will not be enough in the future, says Mikko Kuivaniemi, Head of Power System Reserves, at Fingrid.

1. What happens if the power system’s frequency is not stable?

The devices connected to the power system are designed for a specific frequency and can only withstand certain frequency deviations. If the frequency deviates too much, power plants in particular must be disconnected from the power system to prevent them from being damaged.

A domino effect would occur if the frequency deviations were large enough to disconnect power plants from the grid. In the worst case, it would take down the entire system.

2. What causes the power system’s frequency to fluctuate?

Fluctuations are caused by normal variations in electricity consumption and generation that cannot be predicted and balanced in advance. Consumption always fluctuates somewhat, and reserves balance out these variations. In the future, electricity will be increasingly produced using weather-dependent solar and wind power, and the weather cannot be accurately forecast. This causes also normal fluctuations in the power balance.

Faults cause the largest frequency deviations. For example, the sudden failure of an inter-connector or a major power plant could cause significant frequency deviations.

3. Why is the need for reserves constantly increasing, and what are the consequences?

More and more reserves are needed due to the energy transition. Production is increasingly variable, more large demand facilities are arising, transmission connections are growing, and some production units with reserve providing capabilities have left the market. Imbalances between electricity production and consumption are more likely to arise, and reserves are needed to balance them out.

Currently, there are occasional shortages of reserves. The situation will only become more challenging in the future. We need more reserves to respond to the needs of an evolving power system. We need anyone who is capable to join the reserve market: more wind and solar power and new demand facilities, such as electrolysers and electric boilers. We also need more energy storages.

No individual technology will solve the problem – all units that can adjust their power exchange with the grid should contribute to balancing the power system.

The state of the power system can be tracked online.


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